--- 1/draft-ietf-lsr-isis-srv6-extensions-02.txt 2019-10-04 09:13:12.809279467 -0700 +++ 2/draft-ietf-lsr-isis-srv6-extensions-03.txt 2019-10-04 09:13:12.853280568 -0700 @@ -1,24 +1,24 @@ Networking Working Group P. Psenak, Ed. Internet-Draft C. Filsfils Intended status: Standards Track Cisco Systems -Expires: January 5, 2020 A. Bashandy +Expires: April 5, 2020 A. Bashandy Arrcus B. Decraene Orange Z. Hu Huawei Technologies - July 4, 2019 + October 3, 2019 IS-IS Extension to Support Segment Routing over IPv6 Dataplane - draft-ietf-lsr-isis-srv6-extensions-02.txt + draft-ietf-lsr-isis-srv6-extensions-03.txt Abstract Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological sub-paths, called "segments". Segment routing architecture can be implemented over an MPLS data plane as well as an IPv6 data plane. This draft describes the IS-IS extensions required to support Segment Routing over an IPv6 data plane. @@ -38,21 +38,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on January 5, 2020. + This Internet-Draft will expire on April 5, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -67,43 +67,44 @@ 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. SRv6 Capabilities sub-TLV . . . . . . . . . . . . . . . . . . 4 3. Advertising Supported Algorithms . . . . . . . . . . . . . . 4 4. Advertising Maximum SRv6 SID Depths . . . . . . . . . . . . . 4 4.1. Maximum Segments Left MSD Type . . . . . . . . . . . . . 5 4.2. Maximum End Pop MSD Type . . . . . . . . . . . . . . . . 5 4.3. Maximum T.Insert MSD Type . . . . . . . . . . . . . . . . 5 4.4. Maximum T.Encaps MSD Type . . . . . . . . . . . . . . . . 5 4.5. Maximum End D MSD Type . . . . . . . . . . . . . . . . . 6 5. SRv6 SIDs and Reachability . . . . . . . . . . . . . . . . . 6 - 6. Advertising Locators and End SIDs . . . . . . . . . . . . . . 8 - 6.1. SRv6 Locator TLV Format . . . . . . . . . . . . . . . . . 8 - 6.2. SRv6 End SID sub-TLV . . . . . . . . . . . . . . . . . . 9 - 7. Advertising SRv6 Adjacency SIDs . . . . . . . . . . . . . . . 11 - 7.1. SRv6 End.X SID sub-TLV . . . . . . . . . . . . . . . . . 11 - 7.2. SRv6 LAN End.X SID sub-TLV . . . . . . . . . . . . . . . 13 - 8. SRv6 SID Structure Sub-Sub-TLV . . . . . . . . . . . . . . . 14 - 9. Advertising Endpoint Behaviors . . . . . . . . . . . . . . . 15 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 - 10.1. SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . . 16 - 10.1.1. SRv6 End SID sub-TLV . . . . . . . . . . . . . . . . 16 - 10.1.2. Revised sub-TLV table . . . . . . . . . . . . . . . 17 - 10.2. SRv6 Capabilities sub-TLV . . . . . . . . . . . . . . . 17 - 10.3. SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs . . . . . 18 - 10.4. MSD Types . . . . . . . . . . . . . . . . . . . . . . . 18 - 10.5. Sub-Sub-TLVs for SID Sub-TLVs . . . . . . . . . . . . . 18 - 11. Security Considerations . . . . . . . . . . . . . . . . . . . 19 - 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 20 - 13.2. Informative References . . . . . . . . . . . . . . . . . 22 - - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 + 6. Advertising Anycast Property . . . . . . . . . . . . . . . . 8 + 7. Advertising Locators and End SIDs . . . . . . . . . . . . . . 8 + 7.1. SRv6 Locator TLV Format . . . . . . . . . . . . . . . . . 8 + 7.2. SRv6 End SID sub-TLV . . . . . . . . . . . . . . . . . . 10 + 8. Advertising SRv6 Adjacency SIDs . . . . . . . . . . . . . . . 12 + 8.1. SRv6 End.X SID sub-TLV . . . . . . . . . . . . . . . . . 12 + 8.2. SRv6 LAN End.X SID sub-TLV . . . . . . . . . . . . . . . 14 + 9. SRv6 SID Structure Sub-Sub-TLV . . . . . . . . . . . . . . . 15 + 10. Advertising Endpoint Behaviors . . . . . . . . . . . . . . . 16 + 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 + 11.1. SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . . 17 + 11.1.1. SRv6 End SID sub-TLV . . . . . . . . . . . . . . . . 17 + 11.1.2. Revised sub-TLV table . . . . . . . . . . . . . . . 18 + 11.2. SRv6 Capabilities sub-TLV . . . . . . . . . . . . . . . 18 + 11.3. SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs . . . . . 19 + 11.4. MSD Types . . . . . . . . . . . . . . . . . . . . . . . 19 + 11.5. Sub-Sub-TLVs for SID Sub-TLVs . . . . . . . . . . . . . 19 + 11.6. Prefix Attribute Flags Sub-TLV . . . . . . . . . . . . . 20 + 12. Security Considerations . . . . . . . . . . . . . . . . . . . 20 + 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 + 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 + 14.1. Normative References . . . . . . . . . . . . . . . . . . 21 + 14.2. Informative References . . . . . . . . . . . . . . . . . 23 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction With Segment Routing (SR) [I-D.ietf-spring-segment-routing], a node steers a packet through an ordered list of instructions, called segments. Segments are identified through Segment Identifiers (SIDs). Segment Routing can be directly instantiated on the IPv6 data plane @@ -319,29 +320,56 @@ with SRv6 SID advertisements MUST be the longest match prefix installed in the forwarding plane for those SIDs. There are a number of ways in which this requirement could be compromised o Another locator associated with a different topology/algorithm is the longest match o A prefix advertisement (i.e., from TLV 236 or 237) is the longest match -6. Advertising Locators and End SIDs +6. Advertising Anycast Property + + Both prefixes and SRv6 Locators may be configured as anycast and as + such the same value can be advertised by multiple routers. It is + useful for other routers to know that the advertisement is for an + anycast identifier. + + A new flag in "Bit Values for Prefix Attribute Flags Sub-TLV" + registry [RFC7794] is defined to advertise the anycast property: + + Bit #: 4 (Suggested - to be assigned by IANA) + Name: Anycast Flag (A-flag) + + When the prefix/SRv6 locator is configured as anycast, the A-flag + SHOULD be set. Otherwise, this flag MUST be clear. + + The A-flag MUST be preserved when leaked between levels. + + The A-flag and the N-flag MUST NOT both be set. + + If both N-flag and A-flag are set in the prefix/SRv6 Locator + advertisement, the receiving routers MUST ignore the N-flag. + + The same prefix/SRv6 Locator can be advertised by multiple routers. + If at least one of them sets the A-Flag in its advertisement, the + prefix/SRv6 Locator SHOULD be considered as anycast. + +7. Advertising Locators and End SIDs The SRv6 Locator TLV is introduced to advertise SRv6 Locators and End SIDs associated with each locator. This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236 and 237. -6.1. SRv6 Locator TLV Format +7.1. SRv6 Locator TLV Format The SRv6 Locator TLV has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |R|R|R|R| MTID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Followed by one or more locator entries of the form: @@ -366,52 +394,48 @@ Note that the value 0 is legal. Locator entry: Metric: 4 octets. As described in [RFC5305]. Flags: 1 octet. The following flags are defined 0 0 1 2 3 4 5 6 7 - +-+-+-+-+-+-+-+-+ - |D|A| Reserved | + |D| Reserved | +-+-+-+-+-+-+-+-+ where: D bit: When the Locator is leaked from level-2 to level-1, the D bit MUST be set. Otherwise, this bit MUST be clear. Locators with the D bit set MUST NOT be leaked from level-1 to level-2. This is to prevent looping. - A bit: When the Locator is configured as anycast, the A bit - SHOULD be set. Otherwise, this bit MUST be clear. - The remaining bits are reserved for future use. They SHOULD be set to zero on transmission and MUST be ignored on receipt. Algorithm: 1 octet. Associated algorithm. Algorithm values are defined in the IGP Algorithm Type registry. Loc-Size: 1 octet. Number of bits in the Locator field. (1 - 128) Locator: 1-16 octets. This field encodes the advertised SRv6 Locator. The Locator is encoded in the minimal number of octets for the given number of bits. Sub-TLV-length: 1 octet. Number of octets used by sub-TLVs Optional sub-TLVs. -6.2. SRv6 End SID sub-TLV +7.2. SRv6 End SID sub-TLV The SRv6 End SID sub-TLV is introduced to advertise SRv6 Segment Identifiers (SID) with Endpoint functions which do not require a particular neighbor in order to be correctly applied [I-D.ietf-spring-srv6-network-programming]. SRv6 SIDs associated with a neighbor are advertised using the sub-TLVs defined in Section 6. This new sub-TLV is advertised in the SRv6 Locator TLV defined in the previous section. SRv6 End SIDs inherit the topology/algorithm from @@ -457,41 +481,41 @@ End SIDs which are NOT a subnet of the associated locator MUST be ignored. Multiple SRv6 End SIDs MAY be associated with the same locator. In cases where the number of SRv6 End SID sub-TLVs exceeds the capacity of a single TLV, multiple Locator TLVs for the same locator MAY be advertised. For a given MTID/Locator the algorithm MUST be the same in all TLVs. If this restriction is not met all TLVs for that MTID/ Locator MUST be ignored. -7. Advertising SRv6 Adjacency SIDs +8. Advertising SRv6 Adjacency SIDs Certain SRv6 Endpoint functions [I-D.ietf-spring-srv6-network-programming] must be associated with a particular neighbor, and in case of multiple layer 3 links to the same neighbor, with a particular link in order to be correctly applied. This document defines two new sub-TLVs of TLV 22, 23, 222, 223, and 141 - namely "SRv6 End.X SID" and "SRv6 LAN End.X SID". IS-IS Neighbor advertisements are topology specific - but not algorithm specific. End.X SIDs therefore inherit the topology from the associated neighbor advertisement, but the algorithm is specified in the individual SID. All End.X SIDs MUST be a subnet of a Locator with matching topology and algorithm which is advertised by the same node in an SRv6 Locator TLV. End.X SIDs which do not meet this requirement MUST be ignored. -7.1. SRv6 End.X SID sub-TLV +8.1. SRv6 End.X SID sub-TLV This sub-TLV is used to advertise an SRv6 SID associated with a point to point adjacency. Multiple SRv6 End.X SID sub-TLVs MAY be associated with the same adjacency. The SRv6 End.X SID sub-TLV has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ @@ -552,21 +576,21 @@ SID: 16 octets. This field encodes the advertised SRv6 SID. Sub-sub-TLV-length: 1 octet. Number of octets used by sub-sub- TLVs Note that multiple TLVs for the same neighbor may be required in order to advertise all of the SRv6 End.X SIDs associated with that neighbor. -7.2. SRv6 LAN End.X SID sub-TLV +8.2. SRv6 LAN End.X SID sub-TLV This sub-TLV is used to advertise an SRv6 SID associated with a LAN adjacency. Since the parent TLV is advertising an adjacency to the Designated Intermediate System(DIS) for the LAN, it is necessary to include the System ID of the physical neighbor on the LAN with which the SRv6 SID is associated. Given that a large number of neighbors may exist on a given LAN a large number of SRv6 LAN END.X SID sub- TLVs may be associated with the same LAN. Note that multiple TLVs for the same DIS neighbor may be required in order to advertise all of the SRv6 End.X SIDs associated with that neighbor. @@ -621,29 +645,29 @@ SRv6 Endpoint Function: 2 octets. As defined in [I-D.ietf-spring-srv6-network-programming] Legal function values for this sub-TLV are defined in Section 9. SID: 16 octets. This field encodes the advertised SRv6 SID. Sub-sub-TLV-length: 1 octet. Number of octets used by sub-sub- TLVs. -8. SRv6 SID Structure Sub-Sub-TLV +9. SRv6 SID Structure Sub-Sub-TLV SRv6 SID Structure Sub-Sub-TLV is an optional Sub-Sub-TLV of: - SRv6 End SID Sub-TLV (Section 6.2) + SRv6 End SID Sub-TLV (Section 7.2) - SRv6 End.X SID Sub-TLV (Section 7.1) + SRv6 End.X SID Sub-TLV (Section 8.1) - SRv6 LAN End.X SID Sub-TLV (Section 7.2) + SRv6 LAN End.X SID Sub-TLV (Section 8.2) SRv6 SID Structure Sub-Sub-TLV is used to advertise the length of each individual part of the SRv6 SID as defined in [I-D.ietf-spring-srv6-network-programming]. It has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | @@ -661,21 +685,21 @@ LN Length: 1 octet. SRv6 SID Locator Node length in bits. Fun. Length: 1 octet. SRv6 SID Function length in bits. Arg. Length: 1 octet. SRv6 SID Arguments length in bits. ISIS SRv6 SID Structure Sub-Sub-TLV MUST NOT appear more than once in its parent sub-TLV. If it appears more than once in its parent TLV, the parent TLV MUST be ignored by the receiver. -9. Advertising Endpoint Behaviors +10. Advertising Endpoint Behaviors Endpoint behaviors are defined in [I-D.ietf-spring-srv6-network-programming] and [I-D.ali-spring-srv6-oam]. The numerical identifiers for the Endpoint behaviors are defined in the "SRv6 Endpoint Behaviors" registry defined in [I-D.ietf-spring-srv6-network-programming]. This section lists the Endpoint behaviors and their identifiers, which MAY be advertised by IS-IS and the SID sub-TLVs in which each type MAY appear. @@ -695,150 +719,161 @@ End.DT6 | 18 | Y | N | N | -----------------------|--------------------|-------|-------|-----------| End.DT4 | 19 | Y | N | N | -----------------------|--------------------|-------|-------|-----------| End.DT64 | 20 | Y | N | N | -----------------------|--------------------|-------|-------|-----------| End.OP | 40 | Y | N | N | -----------------------|--------------------|-------|-------|-----------| End.OTP | 41 | Y | N | N | -10. IANA Considerations +11. IANA Considerations This document requests allocation for the following TLVs, sub- TLVs, and sub-sub-TLVs as well updating the ISIS TLV registry and defining a new registry. -10.1. SRv6 Locator TLV +11.1. SRv6 Locator TLV This document adds one new TLV to the IS-IS TLV Codepoints registry. Value: 27 (suggested - to be assigned by IANA) Name: SRv6 Locator This TLV shares sub-TLV space with existing "Sub-TLVs for TLVs 135, 235, 236 and 237 registry". The name of this registry needs to be changed to "Sub-TLVs for TLVs 27, 135, 235, 236 and 237 registry". -10.1.1. SRv6 End SID sub-TLV +11.1.1. SRv6 End SID sub-TLV This document adds the following new sub-TLV to the (renamed) "Sub- TLVs for TLVs 27, 135, 235, 236 and 237 registry". Value: 5 (suggested - to be assigned by IANA) Name: SRv6 End SID This document requests the creation of a new IANA managed registry for sub-sub-TLVs of the SRv6 End SID sub-TLV. The registration procedure is "Expert Review" as defined in [RFC7370]. Suggested registry name is "sub-sub-TLVs for SRv6 End SID sub-TLV". No sub- sub-TLVs are defined by this document except for the reserved value. 0: Reserved 1-255: Unassigned -10.1.2. Revised sub-TLV table +11.1.2. Revised sub-TLV table The revised table of sub-TLVs for the (renamed) "Sub-TLVs for TLVs 27, 135, 235, 236 and 237 registry" is shown below: Type 27 135 235 236 237 1 n y y y y 2 n y y y y 3 n y y y y 4 y y y y y 5 y n n n n 11 y y y y y 12 y y y y y -10.2. SRv6 Capabilities sub-TLV +11.2. SRv6 Capabilities sub-TLV This document adds the definition of a new sub-TLV in the "Sub- TLVs for TLV 242 registry". Type: 25 (Suggested - to be assigned by IANA) Description: SRv6 Capabilities This document requests the creation of a new IANA managed registry for sub-sub-TLVs of the SRv6 Capability sub-TLV. The registration procedure is "Expert Review" as defined in [RFC7370]. Suggested registry name is "sub-sub-TLVs for SRv6 Capability sub-TLV". No sub- sub-TLVs are defined by this document except for the reserved value. 0: Reserved 1-255: Unassigned -10.3. SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs +11.3. SRv6 End.X SID and SRv6 LAN End.X SID sub-TLVs This document adds the definition of two new sub-TLVs in the "sub- TLVs for TLV 22, 23, 25, 141, 222 and 223 registry". Type: 43 (suggested - to be assigned by IANA) Description: SRv6 End.X SID Type: 44 (suggested - to be assigned by IANA) Description: SRv6 LAN End.X SID Type 22 23 25 141 222 223 43 y y y y y y 44 y y y y y y -10.4. MSD Types +11.4. MSD Types This document defines the following new MSD types. These types are to be defined in the IGP MSD Types registry defined in [RFC8491] . All values are suggested values to be assigned by IANA. Type Description ------------------ 41 SRH Max SL 42 SRH Max End Pop 43 SRH Max T.insert 44 SRH Max T.encaps 45 SRH Max End D -10.5. Sub-Sub-TLVs for SID Sub-TLVs +11.5. Sub-Sub-TLVs for SID Sub-TLVs This document creates the following Sub-Sub-TLV Registry within the "IS-IS TLV Codepoints" registry: Registry: Sub-Sub-TLVs for SID Sub-TLVs Registration Procedure: Expert review - Reference: This document (Section 6.2, Section 7.1, Section 7.2). + Reference: This document (Section 7.2, Section 8.1, Section 8.2). This document defines the following Sub-Sub-TLV in the "Sub-Sub-TLVs for SID Sub-TLVs" registry: Type: 1 Description: SRv6 SID Structure Sub-Sub-TLV. - Reference: This document (Section 8). + Reference: This document (Section 9). -11. Security Considerations +11.6. Prefix Attribute Flags Sub-TLV + + This document adds a new bit in the "Bit Values for Prefix Attribute + Flags Sub-TLV" registry: + + Bit #: 4 + + Description: A bit + + Reference: This document (Section 6). + +12. Security Considerations Security concerns for IS-IS are addressed in [ISO10589], [RFC5304], and [RFC5310]. -12. Contributors +13. Contributors The following people gave a substantial contribution to the content of this document and should be considered as co-authors: Stefano Previdi Huawei Technologies Email: stefano@previdi.net Paul Wells Cisco Systems @@ -868,50 +903,50 @@ Robert Hanzl Cisco Systems Millenium Plaza Building, V Celnici 10, Prague 1, Prague, Czech Republic Email rhanzl@cisco.com Ketan Talaulikar Cisco Systems, Inc. Email: ketant@cisco.com -13. References +14. References -13.1. Normative References +14.1. Normative References [I-D.ali-spring-srv6-oam] Ali, Z., Filsfils, C., Kumar, N., Pignataro, C., faiqbal@cisco.com, f., Gandhi, R., Leddy, J., Matsushima, S., Raszuk, R., daniel.voyer@bell.ca, d., Dawra, G., Peirens, B., Chen, M., and G. Naik, "Operations, Administration, and Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane (SRv6)", draft-ali-spring- srv6-oam-02 (work in progress), October 2018. [I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing- - header-21 (work in progress), June 2019. + header-23 (work in progress), September 2019. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", draft-ietf-isis-segment-routing- extensions-25 (work in progress), May 2019. [I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6 Network Programming", draft-ietf-spring-srv6-network- - programming-01 (work in progress), July 2019. + programming-03 (work in progress), September 2019. [ISO10589] Standardization", I. ". O. F., "Intermediate system to Intermediate system intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode Network Service (ISO 8473), ISO/IEC 10589:2002, Second Edition.", Nov 2002. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, @@ -934,35 +969,40 @@ [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, DOI 10.17487/RFC5310, February 2009, . [RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014, . + [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and + U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 + and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, + March 2016, . + [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions for Advertising Router Information", RFC 7981, DOI 10.17487/RFC7981, October 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, . -13.2. Informative References +14.2. Informative References [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf-spring-segment-routing-15 (work in progress), January 2018. [RFC8355] Filsfils, C., Ed., Previdi, S., Ed., Decraene, B., and R. Shakir, "Resiliency Use Cases in Source Packet Routing in Networking (SPRING) Networks", RFC 8355,